Radiant energy signaling system



Feb. 23, 1943. MQND,JR 2,312,093

RADIANT ENERGY SIGNALING SYSTEM Original Filed Nov. 23, 1938 4 Sheets-Sheet 1 INVENTOR J0/l/V HAYS l/AMMOAQJR BY flow-0}, ATTORNEY Feb. 23, 1943. J. H. HAMMOND, JR I 2,312,093

" RADIANT ENERGY SIGNALiNG SYSTEM i/ I $42 13- I4 JOHN /-/A rs MMMa/vaJR.

ATTORNEY Feb; 23, 1943. .1. H. HAMMOND, \JR 2,312,093

RADIANT ENERGY SIGNALING SYSTEM Original Filed Nov. 25, 1938 4 Sheets-Sheet 3 102mm; v 105M108 INV ENTOR ATTORNEY Feb. 23, 1943.

J. H. HAMMOND, JR

RADIANT ENERGY SIGNALING SYSTEM Original Filed Nov. 23, 1938 4 Sheets-Sheet 4 76 6-77 78MB I40 149 150 I43 Hg. 6 u W 141 A a/142 I46\\4H /45 AAAAAA v u JUHA/ HAYS HAMMOA/QJR.

INVENTOR ATTORNEY Patented Feb. 23, 1943 RADIANT ENERGY SIGNALING SYSTEM John Hays Hammond, (in, Gloucester, Mass, as-

signor to Radio Corporation of America, New York, N. Y., a corporation of Delaware Original application November 23, 1938, Serial No.

241,894, now Patent No. 2,272,839, dated February 10, 1942. Divided and this application March 27, 1941, Serial No. 385,456

4 Claims.

This application is a division of United States patent application Serial No. 241,894, filed November 23, 1938, Patent No. 2,272,839, dated February 10, 1942, entitled Radiant energy signaling system.

This invention relates to privacy and selective methods of communication by radiant energy.

The invention provides a novel and improved system in which phase modulations are utilized for signaling,

The invention further provides an improved transmission system for producing two carrier waves of the same frequency, but with different planes of polarization, the phases of the radiations having any desired relations.

7 The invention also provides polarized receiving means which may be rotated so as to eliminate any undesired interference without interfering with the reception of the desired signal.

The present method accomplishes selectivity of transmission against intentional or other interference by similar signals of the same carrier frequency and may be practiced with any type of communication such as continuous wave telegraphy or telephony, facsimile transmission, etc.

The invention also consists in certain new and original features of construction and combinations of parts hereinafter set forth and claimed.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, the mode of its operation and the manner of its organization may be better understood by referring to the following description taken in connection with the accompanying drawings forming a part thereof in which Fig. 1 illustrates schematically one embodiment of the invention as applied to a transmitting and receiving system for polarized waves;

Fig. 2 illustrates diagrammatically one form of transmitter for use in connection with Fig. 1;

Fig. 3 shows a modified form of a transmitting and receiving system;

Fig. 4 shows diagrammatically the circuits of a continuous wave transmitter which may be used in connection with Fig. 3;

Fig, 5 shows a modified form of signaling for use in the continuous wave transmitter; and

Fig. 6 shows diagrammatically the circuits of a continuous wave receiver which may be used in connection with Fig. 3.

Like reference characters denote like parts in the several figures of the drawings.

In the following description and in the claims parts will be identified by specif c names for convenienc but they are intend d to b as eneric in their applicati to sim lar parts as the art will permit.

Referring to the. accompanying drawings and. more particularly to, F g. l a transmitter Ill is p v d d t output terminals. l2. and l Hi. The terminals H and 1.2. are connected to a vertical radiator consisting of a rod l5, which is mounted in but insulated from a reflector [6, The terminals 13 and I4 are connected to a horizontal radiator consisting of a rod I! which i mounted in but insulated from a reflector 1.8. The reflectors l6 and is may be of any suitable type, but are preferably of parabolic section and have the rods l5 and I! located at the loci of these parabolas.

The energies produced by the. transmi te III at the terminals ll, 12 and l3, l4 are of the same frequency and of the same nature as to modulations, keying, etc. but in general will be of different radio phase. The energy produced at the terminals ll and I2 will be utilized to drive the v tical radiator 15 which produces substantially vertically polarized wave shown diagrammatically by the Sinusoidal line 2!]. The energy produced at the terminals 13 and M will be utilized to drive thev horizontal radiator 11 which produces a Substantially horizontally polarized wave shown diagrammatically by he sinusoidal line 2|. It is to be understood that the reflectors l6 and I3 are not essential to the operation of the system but are used to reinforce the strength and polarization of the radiations, While the planes of polarization of the two radi, ations 20 and 2| are shown to be vertical and horizontal respectively, they may be pmdllced at any desired angles by suitably mounting the radiators and reflectOrs.

The radiations 20 and 2i are both directed to a single collecting antenna system 22 which is shown as consisting of a rod 23 mounted in but insulated from a collector 25 which is preferably of parabolic form with the rod 23 mounted at its focus. The antenna system 22 is sup.- ported on a hollow shaft 26 which is rotatably mountedin a bracket 21 secured to a receiver 28. A wheel 29 is fastened to the shaft 26 so that the antenna system 22 may be turned through a range of The rod 23 is connected through the hollow shaft 26 and bracket 21 to the two input terminals 30 and 3| of the receiver 28 which is suitably designed for the reception of the type of signal produced by the transmitter. By rotating the antenna system 22 the receiver 23 may be made to respond to the vertically polarized radiation 20 or to the horizontally polarized radiation 2! or in part to both.

Preferably the transmitter l9 should be so arranged that'at the receiver the vertically polarized radiation 20 differs from the horizontally polarized radiation 2| by 90 electrical degrees, which may be described as a circularly polarized radiation. Under these conditions the amount of signal from the transmitter I9 which actuates the receiver 28 is independent of the angular setting of the collecting antenna system 22. The system, however, may be operated if there is not exactly 90 degrees difference of electrical phase or of the plane of polarization of the two radiations at the receiver, as some energy will be received from the transmitter at any angular position of the collecting antenna system 22.

In the operation of the system the transmitter and receiver circuits are adjusted in the usual way and continuous wave, telephonic, facsimile or any privacy or selective system can be used with the circuits of the receiver 28 suitably coordinated with .the circuits of the transmitter It). The amount of signal received from the transmitter will be substantially independent of the angular setting of the collecting antenna system 22.

- Since interference in general is usually of plane polarizednature it is evident that by rotating the collecting antenna system 22 until its axis is perpendicular to the .plane of polarization of the interference it is possible to eliminate this interference almost entirely without affecting the intensity of the desired signal from the transmitter M). It is thus seen that this arrangement provides a means of transmission and reception quite free from disturbances of plane polarized radiation of thesame frequency and general nature as those being conveyed, thus an added method of selectivity is provided over and above any selectivity which may be provided by the nature of the transmitting and receiving circuits.

Referring to Fig. 2 a transmitter circuit is shown which may be used for producing the energy to excite the two radiators l5 and I! shown in Fig. 1. In the circuit shown in Fig. 2 a source of carrier energy is diagrammatically illustrated at 35, which may be keyed if desired for telegraphicpurposes. The source of carrier energy 35 is connected through a transformer 91 to the grids of two power amplifier tubes 38 and 39 which are biased by a battery 39 with respect to the center tap of a resistor 4| which is bridged across the filaments of the tubes 38 and 39. These filaments are heated by a battery 42.

' The grids of the tubes 99 and 39 are excited in phase quadrature with the same intensity of signal by the use of input elements such as an inductance 95 and a resistor 46 for the tube 38 and a resistor 4'! and a condenser 98 for the tube 39. These input elements are so arranged that the input impedance of the tube 38, shunted by the inductance 55 in series with the resistor 46, represents a degree inductive load, whereas the input impedance of the tube 39, shunted by the resistor 4'! in series with the condenser 46, represents a 45 degree capacitive load. These two load impedances are preferably equal numerically. Because of the different loadings the center of the secondary of the transformer 31 is at radio frequency with respect to ground. In practice the numerical impedances of the input elements 45,

46, 41 and 48 will be small in comparison with the input impedances of the tubes 38 and 39 and therefore these input elements will be chosen of substantially the same numerical impedance at the frequency of operation. The overallload on the secondary of the transformer 31 is a resistance load, but the A. C. voltage from the grid of tube 38 to ground will differ by electrical degrees from the voltage from the grid of the tube 39 to ground.

The output circuits of the tubes 38 and 39 include the primaries of two transformers 59 and 5| which are shunted by condensers 52 and 53 forming two tank circuits 53a and 54. The secondary winding of the transformer 59 is connected to the terminals I l and l 2 of the transmitter I9 and the secondary winding of the transformer 5| is connected to the terminals l3 and M of said transmitter. The output circuits of the tubes 38 and 39 are energized by a battery 55 which is connected in series with a condenser 56. Across the condenser 59 and in circuit with a choke 5'! is the secondary of a transformer 59, the primary of which is shown as connected to a source 59 of modulating energy. When the modulating energy is operative, the carrier energy will in general not be keyed but will be continuously operative. The condenser 56 and choke 51 are used to minimize the flow of energy from the tubes 38 and 39 to the modulation source 59.

The two tank circuits 53a and 54 are tuned to the radio frequency of the transmitter I'll. .As a result of the phase quadrature relation of the grid excitation the plate circuits will also be actuated in phase quadrature, and both output circuits will also be actuated by radio frequencies in phase quadrature, but not at a modulating frequency as represented by the output of the modulator 59.

It is to be understood that the circuit depicted in Fig. 2 is only illustrative and that any other suitable method could be used for producing the same results and that the receiver 28 will be of suitable construction for responding to the system of communication which the circuits shown in Fig. 2 may be organized to create.

In addition to the superselective features achieved by the system depicted in Figs. 1 and 2 it is possible to use the two polarized waves for super privacy purposes by using a transmitter in which the relative phase of the radiations may be changed for purposes of signaling and a receiving system by which the phases of the radiations from the transmitter may be compared.

The general arrangement of such a system is shown schematically in Fig. 3. A transmitter 6|, of the same general type as shown in Fig. 1, is used for producing the two beams of polarized radiation but is provided with a means for shifting the phase relations. The transmitter 6|, shown in plan view, is provided with the output terminals 62, 63, and 65, 66. The terminals 62 and 63 are connected to a vertical rod radiator 61 which is located at the focus of a parabolic reflector 68. The terminals 65 and 66 are connected to a horizontal rod radiator 69 located at the focus of a parabolic reflector 19. The vertical radiator 61 produces a vertically polarized wave indicated by the dotted line H and the horizontal radiator 69 produces a horizontally polarized wave indicated by the sinusoidal line 72.

A receiver 15 is provided with input terminals l6, l1 and l8, 79. The terminals 16 and Hare connected to a Vertical rod antenna 89, located at the focusv of a parabolic collector SI, and used to receive the vertically polarized wavev II. The terminals I-8- and I9 are connected to a horizontal rod; antenna 82, located at the focus of a parabolic collector 83, and used to receive the horizontally polarized wave I2. Signaling is preferably of the continuous wave type, but wave amplitude modulation may be introduced as an aid to privacy if desired. Signaling is accomplished by changing the relative phases of the two radiations II and I2 with the receiver I5 arranged so as to be differently responsive under the two conditions.

A transmitter for producing the desired relative phase shifting is shown in Fig. 4 and is similar to the transmitter shown in Fig. 2 with the exception that keying means are providedfor modifying the phase relations. A single phase source of carrier frequency energy is provided at 85 and is connected through a transformer 85 to the input circuits of two tubes 81 and 88, which are provided with a filament battery 89 and biasing resistor 96 the mid-point of which is connected through condenser 9i and resistor 92 to ground. A suitable polarizing battery 93 and plate battery 95 are also provided. The output circuits of the tubes 81 and 88 are connected to two tank circuits 96 and 9'! comprising condensers 98 and 99 and the primaries of twotransformers I and ID! the secondaries of which are connected to output terminals I92, I03 and I05, I06 respectively which correspond to the output terminals II, I2 and I3, I4 of Fig. 1.

Connected between the grids of the tubes 87 and 38 and ground are two resistors It? and I08 and connected between these grids and the blades of. a reversing switch I09 are two resistors II!) and III, the resistors IE3! and I53 being greater than the resistors H and III. Connected between the contacts of the switch I89 and ground are an inductance H2 and a condenser I I3. The impedances of the resistors H0 and III and of the inductance H2 and condenser II3 are about equal. The reversing switch I99 is operated by a polarized relay I I5 the armature coil of which is connected to a reversing switch IIG. One pole of this switch is connected through two oppositely polarized batteries Ill and I18 to the blades of a double pole double throw switch H9. The left hand contacts of the switch 'I I9 are connected to the contacts of a double acting key E29 the armature of which is normally held in a central position. The right hand contacts of the switch H9 are connected to the contacts of a single acting key I2I which is normally held in the up position.

In the operation of the transmitter shown in Fig. 4 when the switch H5 is thrown to the left the key I20 is put into operation. With the key in-the central position as shown no current will flow through the armature winding of the relay II5 so that the switch I85 will be held in the central position as shown. The paths from the grids of tubes 81 and 88 to ground will then be through resistors I91 and IE8 inwhich case the two grids will be excited in phase opposition; these impedances serving to maintain the grid bias and excitation under these conditions. The grid energy is thus repeated into the plate circuits and then through the tank circuits 96 and !-!'I and the transformers IUI and IE2 to the twosets of output terminals I92, I93 and I05, I05. From these the energy passes to the radiators s1 and 69 shown in Fig. 3 where it is radiated as vertically' and horizontally polarized waves, the phases of which are ,equal or in opposition according to the terminology arbitrarily setup f or'designatingequality of phase.

When the key I20 is depressed a circuit. from the battery H8 is closed through the armature winding of the relay II5 causing this armature of the relay II5 to be moved to the left which in turn moves the switch I09 to the left. This causes the resistor I01 to be shunted by the re"- sistor I I0 and inductance I I2and the resistor I08 to be shunted by the resistor III and condenser II3. This makes an inductive impedance from the grid of the tube 81 to ground and a capacitive impedance from the grid of the tube 88 toground. This causes the phase of the radiation generated by the tube 81 to be advanced 45 electricaldegrees and the phase of the radiation: generated by the tube 88 to be retarded 45 electrical degrees; so that the radiation emitted by the radiator 61 leads the radiation emitted by the radiator 69 by electrical degrees.

When the key I25 is elevated the battery iii! will be thrown in circuit with the armature winding of the relay I I5, thus reversing the cur rent through this winding and causing the armature to move to the right time throwing the switch I89 to the right. This will reverse the action just described and produce a capacitive impedance from the grid of the tube 81:- to ground and an inductive impedance from the grid of the tube 88 to ground. will cause the radiation emitted by the radiator 6'1 to'lag' 90 electrical degrees behind the radiation of the radiator 59.

When it is desired to use the key ial'the'doin ble pole switch I I9 is thrown to the right; Underthese conditions a circuit is normally closedfrom the battery II'I through the. armature winding of the relay II5, which causes the switch Ital-.0: be thrown to the right. This, as already de-- scribed, causes the radiation of vertically. and" horizontally polarized waves from the radiators 61 and 59 respectively, the former lagging beehind the latter by 90 electrical degrees. When, the key I2I is depressed a circuit will be closed: from the battery H8 through the armature winding of the relay H5 causing the switch H39 tobe thrown to the, left, which, as alreadyv described causes the vertically polarized'wave. to lead by 90 electrical degrees the horizontally po larized wave. The action of the key 28 and. I2! may be reversed by throwingthe reversing switch H5 into the opposite position.

When operating the key I29 telegraphic code may be sent by using one position of the key fon dashes and the other position for dots regardless of the extent of contact. With the key I21: operative dots and dashes are sent depending upon the lengths of time that the key isdepressed. The transmitter shown in Fig. 4'. thus provides for both types of keying therevers'eing switch IIG providesa choice of correlations of key contacts and relative output phases:

With a transmitter as shown in Fig. 4 and suitably set up for 9D degrees'phase lead or'lag. of one radiation with respect to the other and with the radiations plane polarized at 90'cle grees in space the resulting radiations are ctr cularl polarized with one direction of rotation. with the key on one contact and with the. opposite direction of rotation-with the key on the other contact. A standardcontinuouswave're ceiver cannot distinguish any difference be-* tween these two forms of polarization, while a' suitably constructed receiver'can so distinguish:

Inzcase the radiations are'not' exactly circus larly polarized, but are eliptically polarized, it might be possible to distinguish between the two directions of rotation by the strength of the signals under the two conditions. For this reason it may be advantageous to provide in the carrier source 85 a keying arrangement for varying the carrier strength abruptly at dot and dash rates so that the true signals sent by the key E28 or key I 2| cannot be distinguished on the basis of differences of signal strength, but must be distinguished on the basis of phase relations.

Instead of using the abrupt keying arrangements shown in Fig. 4 a continuous phase shifting arrangement may be used as shown in Fig. 5. In this figure the tubes 81 and 88 are identical with the tubes 81 and 88 of Fig. 4 and their output circuits would be connected through the transformers I88 and NH to the output terminals I02, I93 and I85, I86 as shown in that figure.

In Fig. 5 a three coil arrangement is provided which comprises two fixed coils I25 and I26 coupled to a rotatable coil I 21. The grid of the tube 81 is connected to the rotatable coil I21 and the grid of the tube 88 is connected to a tap on the fixed coil I26. Phase splitting circuits including two resistors I28 and I29 and a condenser I3II are connected to the fixed coils I25 and I26 and a single phase source of carrier frequency energy I 3I is provided which is similar to that shown at 85 in Fig. 4. The coils I25 and I26 are so arranged with their axes at right angles that they produce a so-called rotating field analagous to that of a two phase induction motor in which the currents in the coils differ by 90 electrical degrees. The rotatable coil I21 is mounted in this rotating field and is operatively connected to a key I32 in such a way that when this key is depressed it will cause the coil I21 to be rotated in one direction and when it is elevated it will cause the coil I21 to be rotated in the other direction. Stops I35 and I38 are provided so that the coil I21 is rotated through the desired angles when the key I32 is depressed or elevated. The arrangement of the circuits is "a such that the voltages impressed on the grids of the two tubes 81 and 88 are substantially equal in magnitude regardless of the angular setting of the coil I 21.

In the operation of the modified form of the 4 coils I25 and I26 and will cause the wave generated by the tube 81 to lead the wave generated by the tube 88 by an amount dependent upon the rotation of the coil I21. When the key I32 is elevated the reverse action will take place and the wave generated by the tube 81 will lag behind the wave generated by the tube 88 an amount dependent upon the rotation of the coil I21. In this way the keying may be accomplished by rotating the coil I21 in one direction for a dash and the other direction for a dot. Remote control of the keying system may be provided if desired.

The difference of electrical angular displacement between the two waves need not be 90 electrical degrees but may be much smaller, the minimum depending in part on the sensitivity of the receiving device as a detector of phase shifts. In order to prevent the rotation of the coil I21 from being noted at an ordinary receiver because of any slight amplitude modulation or slight phase or frequency modulation which may be produced in the wave radiated by one of the tubes 81 or 88, it may be desirable to vary the frequency, amplitude or frequency and amplitude of the carrier source I3I sufficiently at keying rates so that as a practical matter the motion of the key I32 can be determined only by phase comparison of the two radiations.

The receiver 15, shown in Fig. 3, which is used for receiving and interpreting the two polarized waves H and 12 generated by the transmitter shown in Fig. 4 or that shown in Fig. 5; in conjunction with Fig. 4, may be provided with a receiving circuit as shown in Fig. 6. In this circuit the input terminals 16 and 11 are connected through a transformer I48 to a tuned circuit I4I which comprises the secondary of the transformer I48 and a variable condenser I42. The input terminals 18 and 19 are connected through a transformer I43 to a tuned circuit I45 which comprises the secondary of the transformer I43 and a variable condenser I46. The tuned circuits MI and I45 are connected to the first grids of two pentagrid mixer tubes M1 and I48. The ground ends of these circuits are connected through four resistors I49, I58, I81, I86 and a battery I85 to ground and are suitably bypassed to ground by four condensers I5I, I52, I53 and I83.

A source of heterodyning current I55 is provided which is connected through a transformer I56 to the third grids of the tubes I4! and I48. A battery I51 for suitably biasing these grids is connected in the circuit of the secondary of the transformer I56. The second and fourth grids of the tubes I41 and I48 are polarized by two batteries I58 and I59, while the plates of these tubes are further polarized by two additional batteries I60 and I6I which are connected through the primarie of two transformers I52 and I63 and through two radio frequency filters I65 and I66 to these plates. The fifth grids of the tubes I48 and I41 are connected to the cathodes, which may be self-polarized by two condensers I69 and I10.

The secondaries of the transformers I62 and I63 are suitably tapped and connected through two resistors I1I and I 12 to the grids of two audio frequency amplifier tubes I15 and I16. Bridged across a part of the secondary of the transformer I62 is the resistor Ill and an inductor I11 and bridged across part of the secondary of the transformer I63 is the resistor I12 and a condenser I19. The ground ends of the secondaries of the transformers I62 and I63 are connected to ground through two resistor I8I and I82 and the resistor I86 and battery I and are suitably by-passed by two condensers I18 and I83. The plate circuits of the tubes I15 and I16 include two plate batteries I88 and I89 and the primaries of two transformers I98 and I 9| which are shunted by two resistors I92 and I93.

The secondaries of the two transformers I and I9I are connected through a reversing switch I95 to the blade of a single-pole, double-throw switch I96. One contact of the switch I96 is connected to a pair of head phones I91 and the other contact to the plate of a diode rectifier I98. The cathode of this rectifier is connected to the winding of a relay I99 which is shunted by a condenser 288. The front contact of the relay I99 is connected through a transformer 28I to a tone source 29-2 and the back contact is connected through a transformer 203 to a different tone source 205. The secondaries of the two transformers 2-9I and 293 are connected through a pair of head phones 299 to ground.

In the operation of the receiving system shown in Fig. 6 use is made of the fact that if two waves of the same frequency but of different phase are both heterodyned by the same source the resulting beat notes will have the same phase difference as the original waves and involves the use of two receiving devices which are separately actuated :by the two polarized waves and cause two audio frequency currents to be like phased oroppositely phased depending upon which wave leads the other by 90 electrical degrees.

When the two polarized waves 11 and 12 are received by the two rod antennas 85 and 82, shown in Fig. 3, the signals will be impressed upon the input terminals 16, 11 and 18, 19. From these terminals the signals will pass through the transformers I59 and I43 (Fig. 6) to the tuned circuits MI and M and will be impressed upon the first grids of the tubes I 51 and I 38. The input signals are heterodyned to audio or other low frequency by the oscillator I55 which impressescorresponding voltages on the third grids of the pentagr id tubes 1-4-1 and I49. The detected output currents from the tubes I51 and I48 will pass through the radio frequency filters I65 and I56 and will actuate the transformers I62 and I63 with audio or other low frequency currents.

Thesecircu-its are of a well known arrangement for frequency changing purposes and the relation between the output current and input voltage is given by the equation in which i is the plate current; e1 and ex are the voltages impressed on the first and third grids respectively and all the other letters represent constants. The output audio currents arise from the term Q8163.

Let

e1=m sin of for the tube 141 e1=m sin (wt-lb) for the tube I48.

Let

e3=n sin (av-17) t for both tubes where m and 'n are constants c: and p refer to radio .and audio frequencies and is the phase difference between -e1 for tube I41 and c1 for tube It is evident therefore that if the voltages impressed on .thegridsof the tubes I41 and I48 correspond to those on the grids of the tubes 81 and 88 (Figs. 4 and 5) then the difference of phase of the audio currents at the transformers I62 and I63 will be the same as the differences of the radio phases. In place of comparing the radio phases of the voltages it is only necessary to compare the phases of the detected currents.

The audio circuits are so designed as to produce a phase shift of i5 electrical degrees in opposite senses in the two channels so that a net differential shift of 99 electrical degrees occurs in the audio circuits. As a result the audio currents become in phase with each other or out of phase with each other depending on which of the radio channels leads the other by 90 electrical de- 'plified in the platecircuit of the tubes I15 and I16 and are impressed through the transformers I90 and I'9I upon the combining circuit including the head phones I91 or the rectifier I 98.

Automatic volume control may be used for making the Voltage outputs of the transformers I99 and I9I substantially equal in magnitude. This may be accomplished by the signal currents which are rectified by the anodes of the tubes I15 and I-16 from the grid transformer and which develop automatic bias voltage across the bias resistor I86 which is applied to the control grids of all the tubes. The battery I causes the automatic volume control to be inoperative unless a satisfactory signal exists.

The rectified voltage developed across the resistor I86 is impressed through the resistors I81, I49 and I59, suitably by-passed and filtered by the condensers I93, I5I, I52 and I55, to control the grid bias of the tubes I41 and I48, so that the audio voltages at the transformers I62 and I63 are a slowly increasing function of the signal voltages. The voltage across the resistor I86, supplemented by the voltage across the resistor 'I'BI ,controls the bias on the tube I15 and the voltage across the resistor I85 supplemented by the voltage across the resistor I32 controls the bias on the tube I16.

In this way increasing signals at the transformers I62 and I65 decrease the gain ratios of the tubes I15 and "I15. This volume control is so designed that the audio outputs at the transformers I99 and I9I are substantially the same and are of a definite amount regardless of the total signal strength impressed on the two channels or of considerable differences of signal strength.

It is therefore evident that two substantially equal audio voltages result at the secondaries of the transformers I99 and I91, the phases of which are dependent on the keying positions at the transmitter shown in Figs. 4 and 5. With the keys in the neutral position the voltages at the output sides of the transformers I99 and 'I9'I will differ in phase by 90 electrical degreea'but with the keys in the operative positions the phase difference of these audio voltages will become zero or degrees, depending on the position of the keys and the setting of the switch II6 of Fig. 4. By operating the reversing switch I95 the outputs of the two transformers I90 and I9I may be made additive, for example when the key I2!) is down, and subtractive when it is up. The two reversing switches I I6 and I95 may be coordinated and synchronously thrown from time to time to change the correspondence of phases and signals as desired.

The selector switch I96 may be thrown to the left for indicating the combined signals in the head phones I91 in response to the operation of the key I2I at the transmitter. With the key IZI in the down position the voltages combine to produce a loud signal and with the key in the up position the voltages oppose to produce a small or zero signal. For indicating in response to the operation of the key I29 at the transmitter the switch may be thrown to the right. The signal will then be impressed on the diode rectifier I98 which will produce a direct current in the winding of the relay I99 the strength of which is controlled by the position of the key I20 at the transmitter. Thus when the key I20 is in the down position a strong current will pass through the winding of the relay I99 thus moving its armature to the right which will close a circuit from the tone source 202 through the head phones 200 producing a given tone in these phones. When the key I20 is in the up position a weak current will pass through the winding of the relay I99 which will not be sufficient to operate this relay so that the tone source 205 will be thrown in circuit with the head phones 206 to produce a different tone in these phones. The relay I99 will be operated in a similar manner when the key I32 in Fig. is operated. It is thus seen that the position of the key I20 or the key I32 would be indicated by the tonal value of the sound in the head phones 206.

It is to be understood that the relative phases of the currents at the receiver may be compared in other ways than that described. For example the secondaries of the transformers I90 and IBI may be connected to the deflecting plates of a cathode ray oscillograph yielding a circular diagram with the key I20 in a neutral position, a vertical line when the key is down and a horizontal line when it is up.

Another method may use receivers in which an intermediate frequency circuit is placed between the radio and audio frequency circuits.

It is also to be understood that for receiving the waves generated by the system shown in Fig. 1 the audio outputs of the tubes I41 and I49 may be combined to make a so-called rotating magnetic field in which may be mounted an adjustable, rotatable secondary, suitably connected to an audio amplifier. This rotatable secondary would pick up the signals from the transmitter shown in Fig. 1 in any position, but for superselectivity purposes it would be so adjusted as to minimize the effects of any plane polarized radiation constituting interference.

Although only a few of the various forms in which this invention maybe embodied have been shown herein, it is to be understood that the invention is not limited to any specific construction but may be embodied in various forms without departing from the spirit of the invention or the scope of the appended claims.

What I claim is:

1. In a signaling system which includes a transmitter and a receiver, said receiver being provided with a signal receptor, the method of minimizing interference in a given plane of polarization which comprises, transmitting the signal energy as two independent plane polarized phase displaced waves having mutually perpendicular planes of polarization to provide a substantially circularly polarized transmitted wave, intercepting the transmitted waves, and orienting the receptor to a position which is substantially perpendicular to the plane of polarization of the interference wave.

2. In a radio signaling system adapted for signaling over a path which is so short that the polarization of the transmitted waves is substan tially unaffected by the transmission medium, said system including means for transmitting signaling energy as a substantially circularly polarized wave and a receiver including an antenna structure adapted to be unresponsive to waves having a certain polarization relative to the receiver antenna structure, said antenna structure being arranged to be adjustably orientated with respect to the plane of polarization of received waves, the method of eliminating interference with desired signals caused by undesired plane polarized waves which consists in adjusting the receiving antenna structure to the orientation at which it is nonresponsive to said interfering waves but fully responsive to that component of the circularly po larized wave which is at right angles to the plane of polarization of the undesired wave.

3. In a short wave radio signaling system adapted for signaling over a path which is so short that the polarization of the transmitted waves is substantially unaffected by the transmission medium, said system including means for transmitting signaling energy as a substantially circularly polarized wave and a receiver including an antenna structure adapted to be unresponsive to waves having a certain polarization relative to the receiver antenna structure, said antenna structure being arranged to be adjustably orientated with respect to the plane of polarization of received waves, the method of eliminating interference with desired signals caused by undesired plane polarized waves which consists in adjusting the receiving antenna structure to the orientation at which it is non-responsive to said interfering waves but fully responsive to that component of the circularly polarized wave which is at right angles to the plane of polarization of the undesired wave.

4. In a short wave radio signaling system adapted for signaling over a path which is so short that the polarization of the transmitted waves is substantially unaffected by the transmission medium, means for transmitting signaling energy as a substantially circularly polarized wave, a receiver including an antenna structure adapted to be unresponsive to waves having a certain polarization relative to the receiver antenna structure, and means for orientating said antenna structure with respect to the plane of polarization of received waves, to a position at which it is non-responsive to undesired plane polarized interfering waves but fully responsive to that component of the circularly polarized wave which is at right angles to the plane of polarization of the undesired wave.

JOHN HAYS HAMMOND, JR. 

